causal pathway scraping: emit markdown or html fragments

[grosscol]

Emit markdown content into the _casual_paths directory

Update knowledge base layout to incorporate individual causal pathway entries into examples list. Something along the lines of:

{%- for cp in site.causal_paths -%}
  <details>
    <summary><b>{{post.title}}</b></summary>
   ...
  </details>
{%- endfor -%}

Part of #8